1. Field of the Invention
The present invention relates to a gas sensor element, to a gas sensor, and to a method of manufacturing a gas sensor element.
2. Description of the Related Art
A gas sensor is used for combustion control for an internal combustion engine. The gas sensor includes a gas sensor element that outputs a detection signal indicative of the concentration of a particular component (e.g., oxygen) of exhaust gas emitted from the internal combustion engine. For example, a gas sensor element described in Patent Document 1 includes alumina sheets each having a through hole extending in a thickness direction, and a zirconia filling portion having oxygen ionic conductivity is embedded in each of the through holes. A pair of electrodes are disposed on opposite surfaces of each zirconia filling portion. Patent Document 1 shows a structure in which the thickness of the zirconia filling portion is made larger than the depth of the through hole (i.e., the thickness of the alumina sheet) such that the zirconia filling portion protrudes from the through hole, and the size of the protruding portion of the zirconia filling portion is made larger than the opening area of the through hole.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2010-145214
3. PROBLEMS TO BE SOLVED BY THE INVENTION
Generally, wiring layers (conductor layers) for outputting an electric signal from the electrodes disposed on the zirconia filling portion to the outside of a sensor element are disposed on the alumina sheet. However, in Patent Document 1, there is no disclosure concerning such wiring layers. With the structure of the zirconia filling portion shown in Patent Document 1, when a wiring layer is disposed so as to extend from an electrode on the zirconia filling portion to an edge portion of the alumina sheet, the wiring layer may be cracked or broken at an edge of the zirconia filling portion that is located outside the through hole. Therefore, there is a need for a technique capable of suppressing the occurrence of cracking or breakage of a conductor layer including an electrode and a wiring layer in a gas sensor element including an insulating portion having a through hole and an electrolyte portion embedded in the through hole.